Apparatus for evaporative concentration of water to be treated, which uses hot lime softening, and method for evaporative concentration of water using the same

ABSTRACT

An apparatus for evaporative concentration of water, containing hardness-causing substances, to be treated using hot lime softening, includes: a first evaporator configured to form first concentrated water from the water to be treated by evaporatively concentrating the water by first heat exchange with hot steam; a hot lime softener configured to precipitate and to separate hardness-causing substances contained in the first concentrated water from at least a portion of the first concentrated water from the first evaporator by reaction with lime and configured to remove the hardness-causing substances from the first concentrated water; and a second evaporator configured to form second concentrated water by further evaporatively concentrating at least a portion of the first concentrated water that passed through the hot lime softener by second heat exchange with hot steam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/268,985, filed on Sep. 19, 2016, which claims benefit of priority toKorean Patent Application No. 10-2015-0135738 filed on Sep. 24, 2015 inthe Korean Intellectual Property Office, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND 1. Field

Apparatuses and methods consistent with exemplary embodiments relate toa technology for evaporative concentration of water, containinghardness-causing substances, to be treated, and more particularly to anapparatus and method for evaporative concentration of water to betreated, in which the water to be treated is evaporatively concentratedby sequential passage through a first evaporator, a hot lime softenerand a second evaporator so that hardness-causing substances in the waterare effectively removed therefrom by hot lime softening to prevent scaleformation, and in which a separate heat source for satisfying theoperating temperature of the hot lime softener is not required, thusreducing the operation cost.

2. Description of the Related Art

Zero Liquid Discharge (ZLD) systems are processes in which wastewater istreated so that flowback water (water to be treated) or produced waterwill be recycled and a small amount of sludge excluding treated waterwill be discharged to the outside. Recently, companies and academiccircles are becoming more and more interested in Zero Liquid Discharge(ZLD) systems.

There are indications of a gradual increase of the supply price ofindustrial water, a gradual increase of production costs due to anincrease of discharge fees by regulations on total quantity of effluentwater, and a scheduled enactment of a recycling obligation of more than⅓ of effluent discharge flow. Also, companies and academic circles valuejudgments are changing to avoid concerns about environmental pollutionproblems. Recently, there has been a movement to introduce zero liquiddischarge systems not only for specific wastewater but also for allwater.

In foreign countries, ZLD systems have been introduced long ago. InJapan, ZLD systems are currently operated in about 100 places. ZLDsystems in Japan are installed mainly in high-value-added semiconductorplants. As a large amount of high-quality water is required or the areasof installation of ZLD systems correspond to areas such as nationalparks in which discharge of specific pollutants is limited, ZLD systemsthat require high installation and operation costs are introduced andoperated.

Particularly, in the case of Canon Inc. (Oita, Japan) that producescopier cartridge products, Oita was incorporated into total emissionregulation areas, and thus the neighboring fisheries cooperativeassociation requested the prohibition of wastewater discharge in orderto protect fish resources, and for this reason, a ZLD system wasintroduced in Canon Inc. Meanwhile, UMC Japan, a semiconductormanufacturing plant, is located in a fair park, and thus a ZLD systemwas introduced therein.

In the case of the USA, it is estimated that ZLD systems are installedand operated in several thousand places. ZLD systems in the USA havebeen introduced mainly either in area to which strict effluent waterquality standards established by each state are applied, or in plantslocated in areas with poor water supply conditions, such as deserts.

Particularly, La Paloma Plant, a steam power plant located in the middleof the Mojave Desert, Calif., is located in a large agricultural area inwhich effluent water quality standards are very strict and the supply ofwater from areas neighboring the Mojave Desert is poor and also theprice of water is high. For this reason, a ZLD system was introducedtherein, and water recovered from the ZLD system is recycled as boilerfeed water to operate the turbine of the power plant.

In the case of Intel Inc., a semiconductor manufacturing plant, a ZLDsystem was introduced, because emission standards are strict and theArizona area lacks industrial water.

Such ZLD systems are largely classified into reverse osmosis (RO) ZLDsystems that perform separation using osmotic pressure, and thermal ZLDsystems that perform separation by thermal evaporative concentration andphase change.

Among them, the thermal ZLD is principally based on the evaporativeconcentration technology utilized in the 19^(th) century food industry,and intensified environmental regulations leading to increased reuse ofwater resources have increased demands in thermal ZLD technology appliedin various industry fields. The thermal ZLD process using a heat-inducedphase change is most effective for non-degradable wastewater.

In recent years, methods for recovering oil sands as alternativeresources for conventional oils which are becoming more and moreexhausted have been of increasing interest. Particularly, whensteam-assisted gravity drainage (SAGD), which is one of these methods,is used, water treatment using the above-described ZLD system isconsidered a very important process.

This is because water separated in a process of refining recovered oilsands contains contaminants such as silica, and thus causesenvironmental problems when being discharged without treatment, while itis very efficient to purify water separated from oil sands and recyclethe purified water as steam to be injected into oil wells in which oilsands are buried.

Flowback water (or produced water) generated in the process of refiningoil sands as described above is generally separated from sludge by anevaporative concentration process. Herein, hardness-causing substances,such as silica, calcium (Ca) and magnesium (Mg), which are present inthe water to be treated, can be precipitated during the evaporativeconcentration process to cause scale on the overall ZLD system includingan evaporator. For this reason, a technology for controlling suchsubstances has attracted attention.

FIG. 1 schematically shows a system of the related art which inhibitsprecipitation of hardness-causing substances when water to be treated,generated in SAGD systems or the like, is concentrated by evaporation.

Referring to FIG. 1, water to be treated, introduced into an evaporator34 through a water inlet unit 31, is separated into steam and sludge byan evaporative concentration process, and the separated steam and sludgemove to the respective discharge units 35 and 36.

Before the water to be treated is introduced into the evaporator 34, thepH of the water is increased by a basic substance such as sodiumhydroxide (NaOH), injected from a pH-adjusting substance tank 32. Asshown in the graph of FIG. 2, the solubility of silica in water isproportional to pH, and thus precipitation of silica during evaporativeconcentration of the water in the evaporator can be inhibited.

In another embodiment of the technology of the related art, before thewater to be treated is introduced into the evaporator 34, it may besoftened by a lime softener 33. In the lime softener 33,hardness-causing substances such as calcium and magnesium areprecipitated and separated by reaction with a substance such as lime,whereby softening of the water to be treated is achieved.

Specifically, as shown in the following chemical formula 1, carbonate(HCO₃) of calcium reacts with lime (Ca(OH)₂ or CaO) to form insolublecalcium carbonate (CaCO₃), whereby it can be separated.Ca(HCO₃)₂+Ca(OH)₂→2CaCO₃↓+2H₂O  Chemical Formula 1

In addition, as shown in the following chemical formula 2, calciumbicarbonate (calcium sulfate, calcium chloride, etc.) reacts with sodaash (Na₂CO₃) to form calcium carbonate, whereby it can be removed.CaSO₄+Na₂→CO₃↓CaCO₃↓+Na₂SO₄CaCl₂+Na₂CO₃→CaCO₃↓+2NaCl  Chemical Formula 2

Meanwhile, as shown in the following chemical formula 3, magnesiumcarbonate or bicarbonate (magnesium sulfate, magnesium chloride, etc.)reacts with lime to form insoluble magnesium hydroxide (Mg(OH)₂),whereby it can be separated.Mg(HCO₃)₂+Ca(OH)₂→CaCO₃↓+MgCO₃+2H₂OMgCO₃+Ca(OH)₂→CaCO₃↓+Mg(OH)₂↓MgCl₂+Ca(OH)₂→Mg(OH)₂↓+CaCl₂MgSO₄+Ca(OH)₂→Mg(OH)₂↓+CaSO₄  Chemical Formula 3

In the case of silica, it can either adhere to the surface of magnesiumions which are precipitated by the above-described lime softeningprocess or form calcium-magnesium silicate, whereby it can be separatedand removed.

Such lime softening systems can be classified according to operatingtemperature into three types: a cold lime softener (CLS), a warm limesoftener (WLS) and a hot lime softener (HLS). As shown in Table 1 below,the ability to remove hardness-causing substances, which is indicated bythe concentration of hardness-causing substances remaining inlime-softened water, increases as it goes from the cold lime softener tothe hot lime softener. However, the hot lime softener has a disadvantagein that, because it requires a high operating temperature, it requires aseparate heat source.

TABLE 1 Remaining concentration Type of Operating (mg/L) of hardness-lime softener temperature (° C.) causing substance CLS 15 to 60 80 to110 WLS 60 to 85 30 to 50 HLS 90 to 110 15 to 25

In the evaporative concentration system of the related art shown in FIG.1, the cold or warm lime softener is used as the lime softener 33,because there is a limit to pretreating the water, introduced into thelime softener 33, by using an additional heat source. When this cold orwarm lime softener is used, the amount of hardness-causing substancesremoved is smaller than when the hot lime softener is used. Thus, thecold or warm lime softeners has a problem in that it should be usedtogether with the pH-adjusting system as described above so that it caneffectively inhibit scale formation caused by precipitation ofhardness-causing substances.

SUMMARY

The present disclosure is intended to solve problems occurring in theabove-described technology of the related art for evaporativeconcentration of water to be treated containing hardness-causingsubstances, and is also intended to provide an apparatus and method forevaporative concentration of water to be treated, in which a hot limesoftener for removing hardness-causing substances from the water to betreated is used to improve the ability to remove hardness-causingsubstances, so that scale formation can be effectively inhibited withouthaving to use a separate pH adjusting system, and at the same time, aprocess of passing the water to be treated through a first evaporator isfirst performed, thereby eliminating the need for an additional separateheat source for satisfying the operating temperature condition of thehot lime softener.

In one aspect, one or more exemplary embodiments provide an apparatusfor evaporative concentration of water to be treated containinghardness-causing substances. Specifically, one or more exemplaryembodiments provide an apparatus for evaporative concentration of waterto be treated, which uses hot lime softening, the apparatus including:

a first evaporator configured such that the water to be treated isintroduced therein and evaporatively concentrated by exchange with hotsteam to thereby foi n first concentrated water;

a hot lime softener configured such that all or part of the firstconcentrated water is introduced therein and hardness-causing substancescontained in the first concentrated water are precipitated and separatedby reaction with lime, thereby being removed; and

a second evaporator configured such that all or part of the firstconcentrated water that passed through the hot lime softener isintroduced therein and further evaporatively concentrated by heatexchange with hot steam to thereby form second concentrated water.

Herein, the temperature of the first concentrated water that isintroduced into the hot lime softener may be approximately 90° C. to110° C., and the first evaporator may have a concentration factor of5-10.

In addition, the apparatus for evaporative evaporation according to theexemplary embodiment may further include a recycling line that enablesall or part of the first concentrated water and/or the secondconcentrated water to be introduced into the first evaporator or thesecond evaporator so as to be concentrated again.

Meanwhile, the first evaporator and/or the second evaporator may be avertical tube falling film (VTFF) evaporator including a plurality ofevaporation tubes 8 therein and configured such that the water to betreated is evaporated by heat exchange with hot steam supplied to theouter walls of the evaporation tubes while the water flows in the formof a falling film along the inner walls of the evaporation tubes 8.

Furthermore, the first evaporator and/or the second evaporator may be areduced pressure evaporator in which reduced pressure evaporationoccurs.

The apparatus for evaporative concentration according to the exemplaryembodiment may further include a gas-liquid separator configured suchthat steam present as two phases together with the concentrated water inthe bottom of the first evaporator and/or the second evaporator isintroduced therein and water mist remaining in the steam is separatedand removed, and condensed water formed by heat exchange of hot steamsupplied to the first evaporator and/or the second evaporator is sprayedto the steam introduced into the gas-liquid separator so thathardness-causing substances contained in the steam are separated andremoved.

The apparatus according to the exemplary embodiment may further includea compressor configured to compress the steam from whichhardness-causing substances and water mist were removed in thegas-liquid separator and to supply the compressed steam to the firstevaporator 1 and/or the second evaporator.

The gas-liquid separator is preferably a cyclone-type gas-liquidseparator configured such that the condensed water is sprayed in thetangential direction of the inner circumferential surface of thegas-liquid separator and moves in the form of spiral flow along theinner circumferential surface of the gas-liquid separator.

In addition, the gas-liquid separator may include: a chamber having aninternal space configured such that steam is discharged through a steamoutlet at the top and condensed water is discharged through aconcentrate outlet at the bottom; an inlet unit connected to the side ofthe chamber in the tangential direction of the inner circumferentialsurface of the chamber such that the condensed water moves in the formof spiral flow along the inner circumferential surface of the chamber,the inlet unit being configured to spray the condensed water; and ademister disposed in the upper portion of the chamber so as to dividethe internal space of the chamber and configured to remove mistcontained in steam. In addition, the gas-liquid separator preferablyfurther include, in the chamber, at least one barrier 44 for preventingrising of mist contained in the steam.

Herein, the barrier is preferably formed to protrude from the inner wallof the chamber 43 so as to be inclined upward at an angle ofapproximately 90-180°.

In addition, the apparatus for evaporative concentration according tothe exemplary embodiment may further include a heat exchanger in whichthe condensed water formed by heat exchange of hot steam supplied to thefirst evaporator and/or the second evaporator is heat-exchanged with thewater to be treated which is introduced into the first evaporator.

In another aspect, the exemplary embodiment provides a method forevaporative concentration of water to be treated containinghardness-causing substances. Specifically, the exemplary embodimentprovides a method for evaporative concentration of water to be treated,which uses hot lime softening, the method including the steps of: (a)introducing the water to be treated into a first evaporator in which itis evaporatively concentrated by heat exchange with hot steam, therebyforming first concentrated water; (b) introducing all or part of thefirst concentrated water into a hot lime softener in whichhardness-causing substances contained in the first concentrated waterare precipitated and separated by reaction with lime, thereby beingremoved; and

(c) introducing all or part of the first concentrated water, from whichthe hardness-causing substances were removed, into a second evaporatorin which it is further evaporatively concentrated by heat exchange withhot steam, thereby forming second concentrated water.

Herein, the temperature of the first concentrated water that isintroduced into the hot lime softener may be approximately 90° C. to110° C., and the first evaporator may be operated to have aconcentration factor of 5-10.

Meanwhile, step (a) and/or step (c) may include a process in which allor part of the first concentrated water or the second concentrated wateris introduced again into the first evaporator or the second evaporatorso that it is concentrated again.

In addition, the evaporative concentration in step (a) and/or step (c)may be achieved by reduced pressure evaporation.

The method for evaporative concentration according to the exemplaryembodiment may further include a step in which steam present as twophases together with the concentrated water after step (a) and/or step(c) is introduced into a gas-liquid separator in which water mistremaining in the steam is separated and removed, and condensed waterformed by heat exchange of hot steam supplied to the first evaporatorand/or the second evaporator is sprayed to the steam which is introducedinto the gas-liquid separator so that hardness-causing substancescontained in the steam are separated and removed.

Moreover, the method for evaporative concentration according to theexemplary embodiment may further include, before step (a), a step inwhich condensed water formed by heat exchange of hot steam supplied tothe first evaporator and/or the second evaporator is heat-exchanged withthe water to be treated which is introduced into the first evaporator.

In another aspect, the exemplary embodiment provides an apparatus forevaporative concentration of water, containing hardness-causingsubstances, to be treated using hot lime softening, the apparatusincluding: a first evaporator configured to form first concentratedwater from the water to be treated by evaporatively concentrating thewater by first heat exchange with hot steam; a hot lime softenerconfigured to precipitate and to separate hardness-causing substancescontained in the first concentrated water from at least a portion of thefirst concentrated water from the first evaporator by reaction with limeand configured to remove the hardness-causing substances from the firstconcentrated water; and a second evaporator configured to form secondconcentrated water by further evaporatively concentrating at least aportion of the first concentrated water that passed through the hot limesoftener by second heat exchange with hot steam.

A temperature of the first concentrated water that may be introducedinto the hot lime softener may be approximately 90 r to 110° C.

The first evaporator may have a concentration factor of 5-10.

The apparatus may further include a recycling line providing a path forat least a portion of at least one of the first concentrated water andthe second concentrated water to be introduced into the first evaporatoror the second evaporator so as to be concentrated again.

At least one of the first evaporator and the second evaporator may be avertical tube falling film (VTFF) evaporator including a plurality ofevaporation tubes therein and configured to evaporate the water to betreated by heat exchange with hot steam supplied to outer walls of theplurality of evaporation tubes while the water flows in the form of afalling film along inner walls of the evaporation tubes.

At least one of the first evaporator and the second evaporator may be areduced pressure evaporator in which reduced pressure evaporationoccurs.

The apparatus may further include a gas-liquid separator configured toseparate and remove water mist remaining in steam present as two phasestogether with concentrated water at a bottom of at least one of thefirst evaporator and the second evaporator, wherein condensed waterformed by heat exchange of hot steam supplied to at least one of thefirst evaporator and the second evaporator is sprayed to the steam sothat hardness-causing substances contained in the steam are separatedand removed.

The apparatus may further include a compressor configured to compressthe steam from which the hardness-causing substances and the water mistwere removed in the gas-liquid separator and to supply the compressedsteam to at least one of the first evaporator and the second evaporator.

The gas-liquid separator may include a cyclone-type gas-liquid separatorconfigured to spray the condensed water in a tangential direction of aninner circumferential surface of the gas-liquid separator and to movethe condensed water in a form of spiral flow along the innercircumferential surface of the gas-liquid separator.

The gas-liquid separator may include: a chamber having an internalspace, a steam outlet and a concentrate outlet, wherein steam isdischarged through the steam outlet provided at a top of the chamber andthe condensed water is discharged through the concentrate outletprovided at a bottom of the chamber; an inlet unit connected to a sideof the chamber in the tangential direction of the inner circumferentialsurface of the chamber such that the condensed water moves in the formof spiral flow along the inner circumferential surface of the chamber,the inlet unit being configured to spray the condensed water; and ademister disposed in an upper portion of the chamber so as to divide theinternal space of the chamber and configured to remove mist contained inthe steam.

The gas-liquid separator may further include, in the chamber, at leastone harrier configured to prevent the mist contained in the steam fromrising.

The at least one barrier may be configured to protrude from an innerwall of the chamber so as to be inclined upward at an angle ofapproximately 90-180°.

The apparatus may further include a heat exchanger in which condensedwater formed by heat exchange of hot steam supplied to at least one ofthe first evaporator and the second evaporator is heat-exchanged withthe water to be treated which is introduced into the first evaporator.

In another aspect, the exemplary embodiment provides a method forevaporative concentration of water, containing hardness-causingsubstances, to be treated using hot lime softening, the methodincluding: introducing the water to be treated into a first evaporatorin which the introduced water is evaporatively concentrated by heatexchange with hot steam, thereby forming first concentrated water;introducing at least a portion of the first concentrated water into ahot lime softener in which hardness-causing substances contained in thefirst concentrated water are precipitated and separated by reaction withlime, thereby the hardness-causing substances being removed; andintroducing at least a portion of the first concentrated water, fromwhich the hardness-causing substances were removed, into a secondevaporator in which the at least a portion of the first concentratedwater, from which the hardness-causing substances were removed, isfurther evaporatively concentrated by heat exchange with hot steam,thereby forming second concentrated water.

A temperature of the first concentrated water that is introduced intothe hot lime softener may be approximately 90° C. to 110° C.

The first evaporator may be operated to have a concentration factor of5-10.

At least one of the introducing the water to be treated into the firstevaporator and the introducing the at least a portion of the firstconcentrated water, from which the hardness-causing substances wereremoved includes a process in which at least a portion of the firstconcentrated water or the second concentrated water is introduced againinto the first evaporator or the second evaporator so that it isconcentrated again.

The evaporative concentration in at least one of the introducing thewater to be treated into the first evaporator and the introducing the atleast a portion of the first concentrated water, from which thehardness-causing substances were removed may be performed by reducedpressure evaporation.

The method may further include introducing steam present as two phasestogether with the concentrated water after at least one of theintroducing the water to be treated into the first evaporator and theintroducing the at least a portion of the first concentrated water, fromwhich the hardness-causing substances were removed into a gas-liquidseparator in which water mist remaining in the steam is separated andremoved, wherein condensed water formed by heat exchange of hot steamsupplied to at least one of the first evaporator and the secondevaporator is sprayed to the steam which is introduced into thegas-liquid separator so that hardness-causing substances contained inthe steam are separated and removed.

The method may further include, before the introducing the water to betreated into the first evaporator, heat-exchanging condensed waterformed by heat exchange of hot steam supplied to at least one of thefirst evaporator and the second evaporator with the water to be treatedwhich is introduced into the first evaporator.

According to the exemplary embodiment, water to be treated isevaporatively concentrated by sequential passage through the firstevaporator, the hot lime softener and the second evaporator so thathardness-causing substances are effectively removed therefrom by hotlime softening to thereby prevent scale formation, and which do notrequire a separate heat source for satisfying the operating temperatureof the hot lime softener, thus reducing the operation cost.

In addition, because water to be treated is evaporatively concentratedthrough the first evaporator while the flow rate thereof is reduced, thecapacity of the hot lime softener and the amount of lime introduced intothe hot lime softener can be reduced. In addition, because concentratedwater from which hardness-causing substances were almost removed isintroduced into the second evaporator, a relatively low-grade materialmay be applied to the second evaporator, thus reducing equipment costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a system of the related art which inhibitsprecipitation of hardness-causing substances when water to be treated isconcentrated by evaporation.

FIG. 2 graphically shows the correlation between the solubility ofsilica in water and pH.

FIG. 3 schematically shows an apparatus for evaporative concentration ofwater to be treated, which uses hot lime softening, according to anexemplary embodiment.

FIG. 4 schematically shows an apparatus for evaporative concentration ofwater to be treated, which uses hot lime softening, according to anexemplary embodiment, in which the apparatus further includes recyclinglines.

FIG. 5 schematically shows an example of the structure of a verticaltube falling film evaporator which can be used as a first evaporatorand/or a second evaporator.

FIG. 6 schematically shows a gas-liquid separator according to anexemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, preferred exemplary embodiments will be described in detailwith reference to the accompanying drawings. The terms and words used inthe specification and claims should not be interpreted as being limitedto typical meanings or dictionary definitions, but should be interpretedas having meanings and concepts relevant to the technical scope of theinventive concept.

Throughout the specification, when a first component is referred to asbeing “on” or “under” a second component, it not only refers to a casewhere the first component is directly on the second layer but also acase where a third component exists between the first component and thesecond component.

Throughout the specification, when any part is referred to as comprisingany component, it does not exclude other components, but may furthercomprise other components, unless otherwise specified.

Reference characters used to designate method steps are used forconvenience of explanation, and they do not mean the order of the stepsand the steps may be performed in different orders, unless the order isspecifically stated. That is, the steps may be performed in the orderdescribed and substantially simultaneously, but they may be performed inreverse direction.

It is to be understood that, in the following description, the sameelements will be denoted by the same reference numerals if possible,although they are shown in different drawings. Further, in the followingdescription, the detailed description of known functions andconfigurations herein will be omitted when it may interfere with theunderstanding of the exemplary embodiments.

In addition, terms, such as first, second, A, B, (a), (b) or the likemay be used herein when describing components of the exemplaryembodiment. Each of these terms is not used to define an essence, orderor sequence of a corresponding component but used merely to distinguishthe corresponding component from other components.

It should be noted that if it is described in the specification that onecomponent is “connected,” “coupled” or “joined” to another component, athird component may be “connected,” “coupled,” and “joined” between thefirst and second components, although the first component may bedirectly connected, coupled or joined to the second component.

FIG. 3 schematically shows an apparatus for evaporative concentration ofwater to be treated, which uses hot lime softening, according to anexemplary embodiment.

The apparatus for evaporative concentration of water to be treated,which uses hot lime softening, according to the exemplary embodiment, isan apparatus for evaporative concentration of water containinghardness-causing substances. As shown in FIG. 3, the apparatus of theexemplary embodiment may comprise: a first evaporator 1 configured suchthat water to be treated is introduced therein and evaporativelyconcentrated by exchange with hot steam to form first concentratedwater; a hot lime softener 2 configured such that all or part of thefirst concentrated water is introduced therein and a hardness-causingsubstance contained in the first concentrated water is precipitated andseparated by reaction with lime so as to be removed; and a secondevaporator 3 configured such that all or part of the first concentratedwater that passed through the hot lime softener 2 is introduced thereinand further evaporatively concentrated by heat exchange with hot steamto form second concentrated water.

Water generated in a system such as a SAGD is introduced into the firstevaporator 1 through a water inlet unit 21. Before the water isintroduced into the first evaporator 1, it may pass through a heatingunit such as a heat exchanger 11, whereby it can be preheated forevaporative concentration.

The water introduced into the first evaporator 1 is heat-exchanged withhot steam in the first evaporator 1 while coming into direct or indirectcontact with the hot steam to thereby form first concentrated water, andthe first concentrated water is collected in the bottom of the firstevaporator 1, also called “sump reservoir” and present as two phasestogether with evaporated steam.

As the first evaporator 1 as described above, a vertical tube fallingfilm (VTFF) evaporator may be used. This vertical tube falling filmevaporator includes a plurality of evaporation tubes 8 therein and ischaracterized in that the water introduced into the evaporator isevaporated with heat exchange with hot steam supplied to the outer wallsof the evaporation tubes 8 while it flows in the form of a falling filmalong the inner walls of the evaporation tubes 8.

FIG. 5 shows an embodiment of the vertical tube falling film evaporator.As shown therein, in the vertical tube falling film evaporator, aplate-type flow uniformity unit 42 is horizontally provided at the upperportion of a cylindrical housing 40, and a water inlet 41 is disposed ata level higher than the flow uniformity unit 42. This vertical tubefalling film evaporator may be configured such that the water introducedtherein is supplied to a space S1 upstream of the flow uniformity unit42.

In the housing 40, a plurality of evaporation tubes 8 are denselydisposed. The evaporation tubes 8 are disposed such that the top thereofpasses through the flow uniformity unit 42 and such that the upstreamspace S1 and the internal space 8 communicate with each other. Thus, thewater supplied to the upstream space S1 flows down along the inner wallsof the evaporation tubes 8. While the water that flows down along theinner walls of the evaporation tubes 8 in the form of a falling film isheated by heat exchange with steam, supplied to a heat-exchange space S2in the middle portion of the housing 40, with the walls of theevaporation tubes 8 interposed therebetween, it is evaporated.

This vertical tube falling film evaporator has advantages in that it caninhibit an increase in boiling point without loss of pressure in theapparatus, and can minimize the time of contact with a heating fluidsuch as steam because it shows a very high heat transfer rate even whenthe difference in temperature from the heating fluid is small. Inaddition, it can minimize an increase in the temperature ofheat-sensitive liquid, because a temperature gradient in a liquid filmkept at about 1-2 mm is very small.

Furthermore, the first evaporator 1 may be a reduced pressure evaporatorin which evaporative concentration is performed by reduced pressureevaporation. Preferably, it can achieve evaporative concentration at avacuum of about 10⁻² mmHg or less therein.

Meanwhile, because the water to be treated that is introduced into thefirst evaporator 1 is not subjected to a separate pretreatment processfor hardness-causing substances, it is important to concentrate thewater in such a manner that hardness-causing substances are notprecipitated in the first evaporator 1.

Thus, the water to be treated may be concentrated such that aconcentration factor (obtained by dividing the concentration ofhardness-causing substances in the first concentrated water flowing intothe hot lime softener 2 by the concentration of hardness-causingsubstances flowing into the first evaporator 1) is in a certain range.In this case, precipitation of hardness-causing substances such assilica can be prevented. Preferably, the concentration factor may be5-10.

Herein, the concentration factor of the first evaporator 1 refers eitherto the ratio of the concentration of a concentrate discharged from thefirst evaporator to the concentration of the water flowing into thefirst evaporator 1, or the ratio of the flow rate of a concentratedischarged from the first concentrator 1 to the flow rate of aconcentrate flowing into the first evaporator 1.

All or part of the first concentrated water, obtained by evaporativeconcentration in the first evaporator 1, is introduced into a hot limesoftener 2 and subjected to a lime softening process. Because the firstconcentrated water is heated to a high temperature in the process inwhich it is evaporatively concentrated by heat exchange with hot steamin the first evaporator 1, it can satisfy the operating temperature ofthe hot lime softener 2 without having to use an additional heat source.Herein, the temperature of the first concentrated water that isintroduced into the hot lime softener 2 is preferably in the range ofapproximately 90 to 110° C.

In the hot lime softener 2, hardness-causing substances, such as calcium(Ca) and magnesium (Mg), contained in the first concentrated water, areprecipitated by reaction with lime, whereby they are separated andremoved. In addition, silica adheres to the surface of aggregatedmagnesium ions or forms insoluble calcium-magnesium silicate, whereby itis removed. Specifically, the hot lime softener 2 may comprise: areactor configured such that a precipitation reaction ofhardness-causing substances and lime occurs therein; a precipitatorconfigured such that aggregated particles physically and chemically growtherein; and a clarifier configured such that grown particles areseparated by settlement to thereby provide softened water.

As used herein, the term “lime” is intended to encompass any substances,including lime (CaO), hydrated lime (Ca(OH)₂), soda ash (Na₂CO₃) and thelike, which can induce a precipitation reaction of various salts ofcalcium or magnesium as described above.

After the first concentrated water is subjected to the lime softeningprocess in the lime softener 2 to remove hardness-causing substances, itis introduced into the second evaporator 3 in which it is furtherevaporatively concentrated by heat exchange with hot steam to formsecond concentrated water. Herein, because the first concentrated waterwhich is evaporatively concentrated in the second evaporator was alreadysubjected to the hot lime softening process to remove hardness-causingsubstances, it can be concentrated to saturation without the risk ofscale formation.

This second evaporator 3 may be a vertical tube falling film evaporatorincluding evaporation tubes 8, like the first evaporator 1. It may alsobe a reduced pressure evaporator in which reduced pressure evaporatoroccurs.

The second concentrated water formed by concentration in the secondevaporator 3 may be crystallized through a forced circulation evaporator18, before it is discharged to a concentrated water discharge unit 23.Herein, the forced circulation evaporator 18 may comprise: a heatexchanger configured to heat the second concentrated water by a heatingmedium; and a gas-liquid separator configured to inject the heatedsecond concentrated water into a chamber and evaporate the injectedwater to separate it into steam and a concentrate. The concentratedischarged from the gas-liquid separator is recycled to the heatexchanger by a pump.

As shown in FIG. 3, the apparatus of the exemplary embodiment mayfurther comprise a gas-liquid separator 9 configured such that steampresent as two phases together with concentrated water in the bottom ofthe first evaporator 1 and/or the second evaporator 3 is introducedtherein and water mist remaining in the steam is separated and removed.

In other words, in order to remove water mist and hardness-causingsubstances (such as silica) contained in steam present as two phasestogether with the first concentrated water in the bottom of the firstevaporator 1, the steam is introduced into the gas-liquid separator 9.Herein, condensed water formed by heat exchange of hot steam supplied tothe first evaporator 1 and/or the second evaporator may be sprayed tothe steam introduced into the gas-liquid separator 8 to thereby rinsehardness-inducing substances together with water, wherebyhardness-causing substances contained in the steam can be separated andremoved.

The gas-liquid separator 9 is preferably a cyclone-type gas-liquidseparator 9 in which the condensed water is sprayed in the tangentialdirection of the inner circumferential surface of the gas-liquidseparator 9 and moves along the inner circumferential surface in theform of spiral flow.

As shown in FIG. 6, the cyclone-type gas-liquid separator 9 maycomprise: a chamber 43 having an internal space configured such thatsteam is discharged through a steam outlet 45 at the top and condensedwater is discharged through a concentrate outlet 46 at the bottom; aninlet unit 12 connected to the side of the chamber 43 in the tangentialdirection of the inner circumferential surface of the chamber 43 suchthat the condensed water moves along the inner circumferential surfaceof the chamber 43 in the form of spiral flow, the inlet unit 12 beingconfigured to spray the condensed water; and a demister 16 disposed inthe upper portion of the chamber 43 so as to divide the internal spaceof the chamber 43 and configured to remove mist contained in steam.Herein, the demister 16 may be a mesh-type plate member.

In addition, at least one barrier 44 for preventing rising of mistcontained in the steam produced may be provided in the chamber 43 of thegas-liquid separator 9.

During the production and rising of steam, large and small drops (mist)also rise, and relatively large drops are blocked by the barrier 44 anddescend by gravity.

The barrier 44 is may be provided in the internal space of the chamber43 between the inlet unit 12 and the steam outlet 45, and may be formedto protrude from the inner wall of the chamber 43. More preferably, asshown in FIG. 6, it may be formed to protrude from the inner wall of thechamber 43 so as to be inclined upward at an angle of approximately90-180°. In this case, the rising of mist and the descent of blockedmist can be more effectively induced.

After water and hardness-causing substances such as silica are removedfrom the steam by the gas-liquid separator 9, the steam is introducedinto a compressor 10 in which it is compressed. Then, the compressedsteam is supplied to the first evaporator 1 in which it is used as aheat source for evaporative concentration of water to be treated.

Steam that is generated by evaporative concentration in the secondevaporator 3 may be introduced again into the second evaporator 3 afterpassage through the gas-liquid separator 9 and the compressor 10 asdescribed above, so that it can be used as a heat source. Herein, asingle gas-liquid separator 9 and a single compressor 10 are preferablyused to treat the steams generated in the first and second evaporators 1and 3, but are not limited thereto.

Meanwhile, condensed water that is formed by heat exchange of hot steamsupplied to the first evaporator 1 or the second evaporator 3 may beheat-exchanged in the heat exchanger 11 with the water to be treatedwhich is introduced into the first evaporator 11, before it isdischarged to the condensed water discharge unit 22. In this case, thewater to be treated is pretreated before it is introduced into the firstevaporator 1, and the temperature of the condensed water is reducedbefore it is discharged to the outside, thus reducing environmentalpollution problems caused by waste heat.

In addition, all or part of the condensed water may be introduced intothe gas-liquid separator 9 as described above so that it may be reusedto remove hardness-causing substances from steam.

FIG. 4 schematically shows an apparatus for evaporative concentration ofwater to be treated, which uses hot lime softening, according to anexemplary embodiment, in which the apparatus further comprises recyclinglines 4 and 5.

As shown in FIG. 4, the apparatus for evaporative concentration of waterusing hot lime softening according to an exemplary embodiment mayfurther comprise: a recycling line 4 through which all or part of thefirst concentrated water may be introduced again into the firstevaporator 1 in which it is concentrated again; and a recycling line 5through which the second concentrated water may be introduced again intothe second evaporator 3.

The recycling lines 4 and 5 as described above make it possible toefficiently perform not only the process in which the first concentratedwater is evaporatively concentrated at a concentration factor at whichhardness-causing substances such as silica are not precipitated, butalso the process in which the second concentrated water is evaporativelyconcentrated to saturation.

Although exemplary embodiments have been described for illustrativepurposes, those skilled in the art will appreciate that variousmodifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the inventive concept asdisclosed in the accompanying claims.

What is claimed is:
 1. An apparatus for evaporative concentration ofwater, containing hardness-causing substances, to be treated using hotlime softening, the apparatus comprising: a first evaporator configuredto treat the water by evaporatively concentrating the water by firstheat exchange with hot steam to thereby (i) form first concentratedwater and (ii) reduce an amount of the water to be introduced to a hotlime softener, wherein the first evaporator is disposed before the hotlime softener such that the first concentrated water is introduced tothe hot lime softener to increase precipitation of hardness-causingsubstances contained in the first concentrated water without anadditional heat source used for satisfying operating temperaturecondition of the hot lime softener; the hot lime softener configured to:precipitate and separate the hardness-causing substances from at least aportion of the first concentrated water from the first evaporator byreaction with lime, wherein an amount of the lime is determined based onthe reduced water introduced from the first evaporator, and remove thehardness-causing substances from the first concentrated water; and asecond evaporator configured to form second concentrated water byfurther evaporatively concentrating at least a portion of the firstconcentrated water that passed through the hot lime softener by secondheat exchange with hot steam.
 2. The apparatus of claim 1, wherein atemperature of the first concentrated water that is introduced into thehot lime softener is approximately 90° C. to 110° C.
 3. The apparatus ofclaim 1, wherein the first evaporator has a concentration factor of5-10.
 4. The apparatus of claim 1, further comprising: a recycling lineproviding a path for at least a portion of at least one of the firstconcentrated water and the second concentrated water to be introducedinto the first evaporator or the second evaporator so as to beconcentrated again.
 5. The apparatus of claim 1, wherein at least one ofthe first evaporator and the second evaporator is a vertical tubefalling film (VTFF) evaporator comprising a plurality of evaporationtubes therein and configured to evaporate the water to be treated byheat exchange with hot steam supplied to outer walls of the plurality ofevaporation tubes while the water flows in the form of a falling filmalong inner walls of the evaporation tubes.
 6. The apparatus of claim 1,wherein at least one of the first evaporator and the second evaporatoris a reduced pressure evaporator in which reduced pressure evaporationoccurs.
 7. The apparatus of claim 1, further comprising: a gas-liquidseparator configured to separate and remove water mist remaining insteam present as two phases together with concentrated water at a bottomof at least one of the first evaporator and the second evaporator,wherein condensed water formed by heat exchange of hot steam supplied toat least one of the first evaporator and the second evaporator issprayed into the steam so that hardness-causing substances contained inthe steam are separated and removed.
 8. The apparatus of claim 7,further comprising: a compressor configured to compress the steam fromwhich the hardness-causing substances and the water mist were removed inthe gas-liquid separator and to supply the compressed steam to at leastone of the first evaporator and the second evaporator.
 9. The apparatusof claim 7, wherein the gas-liquid separator comprises a cyclone-typegas-liquid separator configured to: spray the condensed water in atangential direction of an inner circumferential surface of thegas-liquid separator; and move the condensed water in a form of spiralflow along the inner circumferential surface of the gas-liquidseparator.
 10. The apparatus of claim 9, wherein the gas-liquidseparator comprises: a chamber having an internal space, a steam outletand a concentrate outlet, wherein steam is discharged through the steamoutlet provided at a top of the chamber and the condensed water isdischarged through the concentrate outlet provided at a bottom of thechamber; an inlet unit connected to a side of the chamber in thetangential direction of the inner circumferential surface of the chambersuch that the condensed water moves in the form of spiral flow along theinner circumferential surface of the chamber, the inlet unit beingconfigured to spray the condensed water; and a demister disposed in anupper portion of the chamber so as to divide the internal space of thechamber and configured to remove mist contained in the steam.
 11. Theapparatus of claim 10, wherein the gas-liquid separator furthercomprises, in the chamber, at least one barrier configured to preventthe mist contained in the steam from rising.
 12. The apparatus of claim11, wherein the at least one barrier is configured to protrude from aninner wall of the chamber so as to be inclined upward at an angle ofapproximately 90-180°.
 13. The apparatus of claim 1, further comprising:a heat exchanger in which condensed water formed by heat exchange of hotsteam supplied to at least one of the first evaporator and the secondevaporator is heat-exchanged with the water to be treated which isintroduced into the first evaporator.
 14. A method for evaporativeconcentration of water, containing hardness-causing substances, to betreated using hot lime softening, the method comprising: treating thewater by evaporatively concentrating the water by first heat exchangewith hot steam to thereby (i) form first concentrated water and (ii)reduce an amount of the water to be introduced to a hot lime softener,wherein the process of forming the first concentrated water is performedto increase precipitation of hardness-causing substances contained inthe first concentrated water without an additional heat source used forsatisfying operating temperature condition for precipitating thehardness-causing substances; introducing at least a portion of the firstconcentrated water into the hot lime softener in which thehardness-causing substances are precipitated and separated by reactionwith lime, thereby the hardness-causing substances being removed,wherein an amount of the lime is determined based on the reduced waterintroduced from the first evaporator; and introducing at least a portionof the first concentrated water, from which the hardness-causingsubstances were removed, into a second evaporator in which the at leasta portion of the first concentrated water, from which thehardness-causing substances were removed, is further evaporativelyconcentrated by heat exchange with hot steam, thereby forming secondconcentrated water.
 15. The method of claim 14, wherein a temperature ofthe first concentrated water that is introduced into the hot limesoftener is approximately 90° C. to 110° C.
 16. The method of claim 14,wherein the first evaporator is operated to have a concentration factorof 5-10.
 17. The method of claim 14, wherein at least one of theintroducing the water to be treated into the first evaporator and theintroducing the at least a portion of the first concentrated water, fromwhich the hardness-causing substances were removed comprises a processin which at least a portion of the first concentrated water or thesecond concentrated water is introduced again into the first evaporatoror the second evaporator so that it is concentrated again.
 18. Themethod of claim 14, wherein the evaporative concentration in at leastone of the introducing the water to be treated into the first evaporatorand the introducing the at least a portion of the first concentratedwater, from which the hardness-causing substances were removed isperformed by reduced pressure evaporation.
 19. The method of claim 14,further comprising: introducing steam present as two phases togetherwith the concentrated water after at least one of the introducing thewater to be treated into the first evaporator and the introducing the atleast a portion of the first concentrated water, from which thehardness-causing substances were removed into a gas-liquid separator inwhich water mist remaining in the steam is separated and removed,wherein condensed water formed by heat exchange of hot steam supplied toat least one of the first evaporator and the second evaporator issprayed to the steam which is introduced into the gas-liquid separatorso that hardness-causing substances contained in the steam are separatedand removed.
 20. The method of claim 14, wherein, before the introducingthe water to be treated into the first evaporator, heat-exchangingcondensed water is formed by heat exchange of hot steam supplied to atleast one of the first evaporator and the second evaporator with thewater to be treated which is introduced into the first evaporator.